1. Field of the Invention
The present invention relates to a printer, facsimile apparatus, multifunction machine or similar image forming apparatus and more particularly to an electrophotographic image forming apparatus configured to directly or indirectly transfer a toner image formed on an image carrier to a sheet, OHP (OverHead Projector) film or similar recording medium. Further, the present invention relates to a process cartridge removably mounted on an electrophotographic image forming apparatus and including at least a developing device and any one of an image carrier, a charger, an image transferring device and a cleaning device.
2. Description of the Background Art
It is a common practice with an electrophotographic image forming apparatus to uniformly charge the surface of a photoconductive drum, photoconductive belt or similar image carrier, which is in rotation, with a charger, expose the charged surface of the image carrier with an optical writing device to thereby form a latent image, deposit toner on the latent image to thereby form a corresponding toner image, and directly or indirectly transfer the toner image to a recording medium with an image transferring device.
Conventional electrophotographic image forming apparatuses include one on which a process cartridge, accommodating some of an image carrier, a charger, a developing device, a cleaning device and other process units, is removably mounted. The process cartridge not only enhances easy, efficient maintenance, but also reduces the overall size of the image forming apparatus.
Today, a tandem, image forming apparatus, for example, is extensively used for producing color images and includes four stations assigned to a respective color each, e.g., a black, a yellow, a cyan and a magenta station. Each of the four stations includes a respective developing device or a respective process cartridge storing a developer of a particular color. In operation, latent images formed on image carriers are developed by toners of different colors of the developing devices or the process cartridges, and the resulting toner images are sequentially transferred to a recording medium one above the other to thereby form a composite full-color image.
A developer is consumed by repeated development and therefore needs replenishment. It has been customary with an image forming apparatus to replenish fresh toner of a particular color to each of the developing devices or the process cartridges or bodily replace each developing device or each process cartridge when the developing device or the process cartridge has run out of toner. However, the replacement of the process cartridges is not practicable unless the user of the image forming apparatus prepares spare developing devices or process cartridges assigned to a respective color each. This forces the user to prepare an exclusive place for storing, e.g., four spare developing devices or process cartridges of different colors beforehand and therefore causes the user to bear a heavy burden.
Moreover, preparing developing devices or process cartridges of different kinds increases the number of parts and therefore requires classification or production adjustment part by part, causing a manufacturer to bear a heavy burden, too, in the aspect of the management of production and parts.
In light of the above, there has been proposed an image forming apparatus of the type using identical developing devices or identical process cartridges. In this case, only carrier grains, forming part of a two-ingredient type developer, are stored in all developing devices beforehand. Such identical developing devices or process cartridges each are mounted to the body of a particular station of a single image forming apparatus or the body of a particular image forming apparatus. Thereafter, toner grains of a particular color are replenished to the respective developing device or process cartridge. However, the problem with this scheme is that when a person dismounts the developing devices or the toner cartridges, each storing the toner grains of the respective color, for a maintenance or similar purpose and again mounts them, the operator is likely to confuse the stations of a single image forming apparatus or the bodies of image forming apparatuses, resulting in the mixture of colors or development in wrong colors and therefore defective images.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication No. 6-258911, 2000-181176 and 8-146744.